Trailers pulled behind vehicles that do not normally pull a trailer, such as passenger cars or pickup trucks, are connected to the tow vehicle with trailer hitches that must be connected to the tow vehicle in such a way as to not interfere with its normal use, such as a passenger car or a pickup truck. Nevertheless, it is necessary for the trailer to be secured very firmly and safely to avoid damage to property or personal injury. The trailer hitch not only must be strong enough to tow the trailer, but in addition it must secure the trailer to the tow vehicle such that it will not come loose during turns, when being towed over bumpy roads, or even when the load is poorly balanced; such as one that would tend to lift the tongue of the trailer away from the connection with the tow vehicle.
In addition to the firm connection between the trailer and the tow vehicle, it is also necessary to provide a means such that the riding lights of the trailer can be accuated by controls within the tow vehicle and, although it is not always present, it is prudent to include some backup connection between the trailer and the tow vehicle.
The most commonly used means for pulling a trailer behind a tow vehicle of the character of a passenger car or pickup truck is a ball and socket connection wherein a ball about 2 inches in diameter and connected along a verticle diameter is fastened preferably to the frame but sometimes to the bumper of the tow vehicle while a cavity or a socket on the tongue of the trailer is adapted to fit snugly over the ball and to be firmly connected to it with some type of latch means that secures the socket around the lower portion of the ball to prevent it from inadvertently being lifted off of the ball.
For a backup safety connection between the trailer and the tow vehicle, it is common to use chains or cables that connect some secure portion of the tow vehicle to some secure portion of the trailer such that if the main connection, for example, the ball and socket connection, fails, the trailer wll not be able to run free on the road, but rather, will be restrained to some path behind the tow vehicle and therefore capable of being steered and stopped.
Although the commercially available trailer hitches and connections between trailers and tow vehicles are quite adequate for performing their task, accidents involving trailers are frequent largely because of carelessness or ignorance in connecting the trailer to the tow vehicle properly.